1. Field of the Invention
This invention is directed to a grinding apparatus for resurfacing of a rubber belt or roller while the belt or roller remains on the production line.
2. Background of the Invention
Sanforizing is a process of finishing fabric that enhances the appearance and feel of the fabric. The process ensures that the fabric will not shrink when laundered. Sanforizing is performed on fabric prior to cutting and assembling clothing. Through the sanforizing process, the fabric is heated and compressed, which causes the fibers to relax, or shrink. In this way, sanforized fabric will resist shrinkage during ironing, wearing, and especially, washing.
A sanforizer employs a seamless or endless rubber belt in a shrink zone as part of the preshrinking process. A typical endless rubber belt will have an inside circumference of 13 feet, a thickness of approximately 2.625 inches, a width of between 60 inches and 144 inches, and a weight of between 1,300 pounds and 1,700 pounds. The belt typically moves through the shrink zone at between 40 yards per minute (ypm) and 100 ypm. In the shrink zone, the belt is subjected to substantial compressive, tensile, and thermal forces. At the nip point, the belt experiences 10,000 pounds of compression per linear inch of width and as much as 22% elongation stretch. Additionally, the belt is exposed to temperatures ranging from 240° F. to 295° F. The high operating speed, extensive stresses, and elevated temperatures deteriorate the surface of the belt during the course of operation. Thus, a typical endless rubber belt will need to be resurfaced every 500,000 yards to 1,000,000 yards. As such, the belt requires resurfacing every 200 to 400 hours of use, resulting in a loss of production hours.
Resurfacing is performed to produce a pattern on the rubber belt surface, such as a scale-like pattern, and to renew the surface rubber's essential characteristics. The scale provides the necessary friction between the fabric and belt to draw the fabric through the sanforizer. The type and depth of the scale on the rubber belt surface affect the traction between the rubber belt and cloth, which is essential to the mechanical compacting of the cloth. Different fabrics can require different scales for proper compaction. The scale also allows for cooling water to be carried by the rubber belt.
Conventional resurfacing techniques involve either on-line or off-line grinders. For instance, off-line stationary lathes can be used to resurface a rubber belt or roller. However, the heavy belt or belt and roller assembly must be removed from the production line and carried to a lathe. This method requires personnel to move products that can weigh over a ton, and this method requires an extended period of downtime for the sanforizing process.
One on-line method for resurfacing belts and rollers is to use another roller with an abrasive grinding surface. Currently, this method is, by far, the most popular method for resurfacing rubber belts. The roller has a size that is approximately the same size as the width of the belt or roller that is to be ground. The roller is filled with a liquid coolant. Strips of silicon carbide grinding cloth are spirally wound around the roller to provide an abrasive surface. As the roller rotates counter to rotation of the belt, the grinding roller abrades the entire width of the belt at the one time. This method also requires the use of a solid lubricant, such as talcum power. Conventionally, up to 50 pounds of talcum powder is required to properly lubricate the resurfacing process.
However, using an abrasive grinding roller has several disadvantages. First, this method typically produces an uneven scale on the belt. Because of the large area of contact between the belt and roller, the belt surface tends to bounce away from the grinding roller, which produces horizontal chatter marks. Second, roller requires an electric motor with 15-25 hp, which increases the energy costs associated with the resurfacing process. Third, this method generates a lot of heat, causing rubber reversion, in which the rubber reverts to the gum state. Reversion causes the surface properties of the belt to change detrimentally. Poor surface properties negatively affect the cloth appearance and necessitate more frequent resurfacing.
Third, the talcum powder is difficult to contain. A large amount of talcum powder is necessary to lubricate the rubber belt and grinding roller. During resurfacing, talcum powder can spread over an area having a radius of 50 feet or more. The powder is an irritant to nearby workers, settles in the surrounding machinery, coats finished fabric, and creates a workplace hazard. In practice, the cleanup procedure for the talcum powder can take several hours after resurfacing.
Finally, the roller grinding method takes at least four hours (sometimes longer than eight hours) to complete. Often, the process has to be stopped so that the grinding cloth can be tightened and so talc and rubber dust can be removed from between the grinding cloth and the roller.
Another, less popular on-line method uses abrasive grinding belts that are essentially akin to belt sanders. The grinding belts are a few inches in width, and the grinding belts traverse the length of the belt or roller. However, grinding belts are known to have a poor rubber removal rate, they generate a large amount of heat (which can lead to rubber reversion and its associated problems), and the grit on the grinding belt quickly builds up rubber shavings.
Thus a need exists in the art for a grinding apparatus that can operate on-line, provide a uniform scale on a rubber belt, minimize sanforizer downtime, reduce energy consumption and labor costs, consistently provide high quality rubber surface, and decrease the amount of cleanup associated with the resurfacing process.